A ratchetable open-ended wrench is known as an improved hand tool which not only achieves the functions of conventional open-ended wrench but also provides the advantage of ratchetable operation. In view of the convenience, efforts and improvements have been made in this field, for example, Patent Nos. TW228757, TW278060, TW327619, U.S. Pat. No. 5,533,428 (WO9615879), TWM310772, U.S. Pat. Nos. 7,111,529, 7,077,035 and 3,165,015. Further, some adjustable spanners are also provided with similar ratchetable operation mechanism, such as Patent Nos. TW501515, TW511564, U.S. Pat. No. 7,010,999, TW262313, and U.S. Pat. No. 2,879,681.
TW228757 discloses an open-ended wrench which allows application of sequential back and forth strokes for driving a screw/workpiece. The wrench relies on a pair of retractable claws/jaws (2, 3) parallel to each other and disposed in the wrench head, which move along the same direction as a pair of drive springs coupled to the claws/jaws. Therefore, TW228757, which is characterized by the retractable claws/jaws (2, 3) moving back or forth along the activation direction of the springs, can rotate a screw clockwise, and turn back in a counterclockwise direction without rotating the screw. However, a wrench needs the counterforce or friction from the retractable claws/jaws, which are abutted against the screw, to tighten or loosen the screw. In this regard, the retractable claws/jaws (2, 3) of the wrench of TW228757 are formed with toothed surfaces which are parallel to each other to contact a parallel pair of sides of the screw so as to rotate the same. The problem with the wrench is that, since the toothed surfaces of the jaws are substantially parallel to each other and are not perpendicular to the screw sides, the tightening/loosening performance of the wrench is poor, and the toothed structure can be easily abraded after long-term usage. Moreover, due to the complicated jaw-pair structure, the jaw opening (the opening between the jaws) of the wrench must be made larger than the size of the screw/workpiece to be driven, and the retractable claws/jaws (2, 3) may be continuously abraded during operation. Therefore, such a wrench is inconvenient in use. Nevertheless, the through slots (111, 121) accommodating the claws/jaws weaken the wrench head structure.
U.S. Pat. No. 5,533,428 (WO9615879) and TW327619 remedy some of the above defects by providing a wrench providing a single L-shaped retractable claw/jaw 15 which moves in the same direction as a driving spring coupled therewith within a slot 23 inward facing a base portion of the wrench driving head which is near a handle 21, with a modified driving head structure. The retractable jaw 15 has a second engaging surface 14 in parallel to a first engaging surface 13 on a first jaw 11. However, the problem with this wrench is that, during the wrench “reverse rotation” at which the nut is not rotated, the wrench cannot be operated smoothly. One reason is that, the wrench reverse rotation is easily held up because a corner 75 of the nut 60 will block the retracting action of the retractable jaw 15 may tend to block the retractable jaw member 15. Though the inventions provide a chamfered edge 16 between forward surface 30 and engaging surface 14 to allow for improved ratchetability of the retractable jaw 15 to alleviate the above problem, there remain some other defects. Specifically, the driving opening of the wrench driving head is characterized by a complicated structure including bearing surface 50 and recesses 51-53 which are not smoothly connected to each other, and the jaw opening must be larger than the nut/screw/workpiece to be driven, which results in an increased weight of the wrench and inaccurate sizing of jaw opening. Besides, since the driving opening is not smoothly contoured with bearing surface 50 and recesses 51-53, during the wrench reverse rotation when the nut is not rotated, a series of sequential partial-turn strokes are required to find different points for force application. This slows the rate of each wrench reverse rotation operation. Therefore, such a wrench is very inconvenient for a professional user.
The aforementioned or similar problems exist in various other conventional wrenches, such as TWM310772, U.S. Pat. Nos. 3,165,015, 7,077,035 and 7,111,529 which use a retractable claw/jaw moving in the same direction as a driving spring coupled therewith. Another common problem of conventional wrenches is that during the tightening/loosening operation, the spring and the retractable claw/jaw directly bear a great torque, which may adversely affect the wrench service life.
U.S. Pat. No. 6,637,300 (TW501515), U.S. Pat. No. 7,010,999 (TW200637692) and TW511564 issued to Arthur Wu disclose ratchetable adjustable spanners which adopt “pivot-type claw/jaws.” In particular, U.S. Pat. No. 6,637,300 discloses slots 14 which laterally penetrate a fixed jaw 11, and rotatable devices (pivoted jaws) 40, 66 with a symmetrical, paired structure pivotally fixed in said two slots 14, so that the rotatable devices 40, 66 can be clamped between stopping portions 15. With the above structure, the wrench can tighten/loosen a screw in one direction, and turn back without rotating the screw in the opposite direction. However, U.S. Pat. No. 6,637,300 has the following disadvantages: (1) The rotatable devices (pivoted claws) 40, 66 are complicated by providing symmetrical, T-shaped and paired structures. (2) The rotatable devices 40, 66 clamped between the two stopping portions 15 cannot be retracted into the slots 14 receiving said rotatable devices 40, 60, so the wrench driving opening must be made larger, which results in an increased weight, and the ratachetable structure can only be used with an “adjustable spanner” instead of an “open-ended wrench.” (3) The springs 50, 67 are disposed on a pivot, so the rebounding force of the rotatable devices 40, 66 is small, and the operation performance is not good. (4) The slot 14 for accommodating the rotatable devices 40, 66 penetrates the head portion of the wrench, which weaken the strength of the wrench head. TW511564 and U.S. Pat. No. 7,010,999 (TW 200637692) change the through slot 14 of U.S. Pat. No. 6,637,300 to an arcuated, C-shaped opening to acquire a higher strength, and change the “rotatable devices (pivoted claws) 40, 66” of TW501515 with “driving rollers” activated by springs. These driving rollers are big, however. To accommodate the “driving rollers,” the fixed jaw must be made larger. Moreover, the above prior arts are only applicable to an adjustable spanner which is equipped with a “moving jaw” and a “worm” so that these elements can actually engage a screw/nut/workpiece. Thus, the whole adjustable spanner with these elements is even more clumsy and inconvenient to operate.
Among various ratchetable wrenches, those with a retractable jaw moving in the same direction as a driving spring coupling therewith are simpler in structure than those with a pivot-type jaw, and thus have a lower cost. However, the conventional design of the former is highly complicated and has the following disadvantages. (1) The retractable jaw must work with a slot penetrating the fixed jaw of the wrench head, which results in a weak wrench head structure that may be easily ruptured under a great torque for a long time. (2) To engage fasteners or workpieces such as screws/nuts, the wrench is provided with a retractable jaw which is usually designed with a complicated engaging surface, or provided with several retractable jaws working together, so the difficulty in and cost of the fabrication are increased. (3) The retractable jaw is not properly designed to bear great force, and is easily broken. (4) The wrench driving opening/fastener room for accommodating a fastener or workpiece such as a screw/nut has a complicated structure, which brings inconvenience during operation.
Therefore, it is necessary to provide a ratchetable open-ended wrench to eliminate the above disadvantages.